Technical Field
This invention relates generally to apparatus and methods for venting, draining, and re-filling fluids from and to a normally sealed system, for example, a nuclear power plant, and more particularly to a pipe cap assembly and related method which simplify, and increase the efficiency, of such operations.
State of the Art
There are many systems that normally operate as a sealed system, including without limitation, nuclear power plants, conventional fossil-fuel power plants, chemical processing plants, and refineries. Often, such sealed systems normally operate under elevated pressures. Scheduled periodic maintenance must be performed to prevent unscheduled outages. In some instances, such maintenance may include conducting test procedures, e.g., monitoring pressures at various points within the sealed system, without actually opening up the sealed system or stopping normal operation. In other instances, periodic maintenance may include stopping normal operations, and opening the system at one or more points to drain fluids, vent gases, flush lines, and/or re-fill lines with fluids. Even when periodic maintenance is performed, unexpected problems can arise that require that the system be taken down for unscheduled maintenance, sometimes known as an “outage”.
As mentioned above, nuclear power plants are one example of a sealed system that requires such maintenance. There are generally two types of nuclear power plants. A first type of nuclear power plant is a pressurized water reactor (PWR) type, wherein a coolant fluid, e.g., water, is circulated through a closed loop in a highly-pressurized primary circuit between the core of a nuclear reactor and one or more steam generators. The super-heated primary coolant, which may reach 300 degrees Centigrade, is used to boil water within the secondary side of the steam generator. The water boiled in the secondary side of the steam generator flows through a secondary circuit that utilizes steam turbines to produce electricity.
The second type of nuclear power plant is known as a boiling water reactor (BWR) type, wherein the reactor core directly heats water which turns to steam used to drive steam turbines; in this type of reactor, the primary and secondary circuits are effectively merged together.
During a refueling and maintenance outage of a nuclear power plant, it is necessary to drain the reactor coolant system pipes, safety injection pipes and supporting systems. Current drain and vent pipes typically include a shut-off valve which terminates in a pipe nipple having a threaded end opposite the valve. A conventional pipe cap is normally tightened over the threaded end of the pipe nipple. Such conventional pipe caps typically have a cylindrical outer surface.
In order to drain the reactor coolant and other fluids from these pipes, the pipe cap must first be removed from the pipe nipple utilizing a pipe wrench. Such conventional pipe caps are occasionally misplaced, or fall into inconvenient places, after removal during maintenance operations; in those instances, valuable time must be spent replacing or retrieving such pipe caps before the system may be re-started.
After removing the conventional pipe cap with the pipe wrench, a temporary cam lock fitting or similar fitting must then be attached to the threaded end of the pipe nipple, and a hose having a complementary cam lock fitting is attached to the temporary cam lock fitting in order to drain the pipe. This is a labor intensive process that must be performed using protective clothing to minimize contamination exposure of workers from the radiation emitted from the nuclear reactor and the fluids that circulate therethrough. Title 10, Part 20, of the Code of Federal Regulations (10 CFR Part 20), entitled “Standards for Protection Against Radiation,” establishes the dose limits for radiation workers. Section 20.1003 sets forth “ALARA” standards (ALARA is an acronym for “as low as (is) reasonably achievable”) requiring nuclear power plant operators to make every reasonable effort to maintain exposures to ionizing radiation as far below the maximum radiation dose limits as practical. Generally speaking, the more time it takes to perform the drain operation, the higher the dose of radiation to which such workers are exposed. Indeed, time of exposure is one of the three critical factors (i.e., time, distance and shielding) when controlling the exposure of nuclear plant workers to radiation. In addition, the longer it takes to drain and re-fill the pipes within the system, the longer is the outage, which often translates into larger losses of revenue.
Accordingly, there is a need in the field of pipe caps used to seal drain pipes and vents within sealed systems, like power plants and the like, for an improved pipe cap that shortens the time needed to drain, vent, and re-fill the pipes within such plants.
There is also a need for an improved pipe cap that may be used to seal, and un-seal, such pipes more quickly and conveniently for improved worker safety and greater profitability.
There is a further need for an improved pipe cap that will not be misplaced, or fall into inconvenient places, during maintenance operations.
There is a still further need for such an improved pipe cap that is relatively inexpensive and simple to manufacture.